1. Field of the Invention
The present invention relates to illuminating units for illuminating products with light supplied through optical fiber to inspect the products for their outward appearances, flaws and the like or detect alignment marks and the like.
2. Description of the Related Art
One known illuminating unit is constructed to illuminate a work with light supplied from a light source unit, such as a halogen lamp, through plural optical fibers, as disclosed in Japanese Patent Laid-Open Gazette No. HEI 5-248820. Such an illuminating unit does not incorporate any light source therein and hence can be reduced in size and weight and can offer improved degree of freedom of installation and the like.
Recently, there are increasing demands for precise inspection requiring bright illumination upon a very small object to be inspected such as a semiconductor chip or upon a very small portion of a work such as a portion of such a semiconductor chip soldered to a printed circuit board. For this reason, the need has arisen for illuminating a portion of concern efficiently with more condensed and brighter light.
In this respect, however, prior-art illuminating units of this type are unsatisfactory in terms of focusing area, condensing efficiency and the like. For example, an illuminating unit disclosed in Japanese Patent Laid-Open No. HEI 5-199442 condenses light only radially of a ring lens and does not condense light circumferentially of the ring lens, though is capable of preventing light from escaping externally by virtue of the ring lens. Thus, this illuminating unit cannot sufficiently focus light onto a very small area.
In the case where light is condensed with lenses attached to optical fibers one by one, on the other hand, it is required that the positional relations between the light-emitting ends of the respective optical fibers and the lenses be uniform throughout. This is because non-uniform positional relation makes condensing of light unfavorable and might give rise to uneven illuminance on a portion illuminated. As the number of optical fibers used increases, it becomes more difficult to establish uniform positional relation between all the optical fiber used and the respective lenses.
Accordingly, it is a major object of the present invention to solve the aforementioned problems at a time by providing an illuminating unit having a simplified structure capable of setting uniform positional relations between the light-emitting ends of optical fibers and respective lenses very easily and precisely as well as of improving light transmission efficiency therebetween as much as possible.